Just as people are living longer than they did in the past, cats are living longer too. In fact, the percentage of cats over six years of age has nearly doubled in just over a decade, and there is every reason to expect that the "graying" cat population will continue to grow.

So how old is my cat, really?

Cats are individuals and, like people, they experience advancing years in their own unique ways. Many cats begin to encounter age-related physical changes between seven and ten years of age, and most do so by the time they are 12. The commonly held belief that every "cat year" is worth seven "human years" is not entirely accurate. In reality, a one-year-old cat is physiologically similar to a 16-year-old human, and a two-year-old cat is like a person of 21. For every year thereafter, each cat year is worth about four human years. Using this formula, a ten-year-old cat is similar age wise to a 53-year-old person, a 12-year-old cat to a 61-year-old person, and a 15-year-old cat to a person of 73.

Advancing age is not a disease

Aging is a natural process. Although many complex physical changes accompany advancing years, age in and of itself is not a disease. Even though many conditions that affect older cats are not correctable, they can often be controlled. The key to making sure your senior cat has the healthiest and highest quality of life possible is to recognize and reduce factors that may be health risks, detect disease as early as possible, correct or delay the progression of disease, and improve or maintain the health of the body's systems.

What happens as my cat ages?

The aging process is accompanied by many physical and behavioral changes:

• Compared to younger cats, the immune system of older cats is less able to fend off foreign invaders. Chronic diseases often associated with aging can impair immune function even further.

• Dehydration, a consequence of many diseases common to older cats, further diminishes blood circulation and immunity.

• The skin of an older cat is thinner and less elastic, has reduced blood circulation, and is more prone to infection.
  

• Older cats groom themselves less effectively than do younger cats, sometimes resulting in hair matting, skin odor, and inflammation.

• The claws of aging felines are often overgrown, thick, and brittle.

• In humans, aging changes in the brain contribute to a loss of memory and alterations in personality commonly referred to as senility. Similar symptoms are seen in elderly cats: wandering, excessive meowing, apparent disorientation, and avoidance of social interaction.

• For various reasons, hearing loss is common in cats of advanced age.

• Aging is also accompanied by many changes in the eyes. A slight haziness of the lens and a lacy appearance to the iris (the colored part of the eye) are both common age-related changes, but neither seems to decrease a cat's vision to any appreciable extent. However, several diseases—especially those associated with high blood pressure—can seriously and irreversibly impair a cat's ability to see.

• Dental disease is extremely common in older cats and can hinder eating and cause significant pain.

• Although many different diseases can cause a loss of appetite, in healthy senior cats, a decreased sense of smell may be partially responsible for a loss of interest in eating. However, the discomfort associated with dental disease is a more likely cause of reluctance to eat.

• Feline kidneys undergo a number of age-related changes that may ultimately lead to impaired function; kidney failure is a common disease in older cats, and its symptoms are extremely varied.

• Degenerative joint disease, or arthritis, is common in older cats. Although most arthritic cats don't become overtly lame, they may have difficulty gaining access to litter boxes and food and water dishes, particularly if they have to jump or climb stairs to get to them.

• Hyperthyroidism (often resulting in overactivity); hypertension (high blood pressure, usually a result of either kidney failure or hyperthyroidism), diabetes mellitus; inflammatory bowel disease; and cancer are all examples of conditions that, though sometimes seen in younger cats, become more prevalent in cats as they age.

Is my cat sick, or is it just old age?

Owners of older cats often notice changes in their cat's behavior, but consider these changes an inevitable and untreatable result of aging, and fail to report them to their veterinarian. Failure to use the litter box, changes in activity levels, and alterations in eating, drinking, or sleeping habits are examples. While veterinarians believe that some behavior problems are due to the diminishing mental abilities of aging cats, it is a mistake to automatically attribute all such changes to old age. In fact, the possibility of some underlying medical condition should always be the first consideration. Disease of virtually any organ system, or any condition that causes pain or impairs mobility can contribute to changes in behavior. For example:

• A fearful cat may not become aggressive until it is in pain (e.g., from dental disease) or less mobile (e.g., from arthritis).

• The increased urine production that often results from diseases common to aging cats (e.g., kidney failure, diabetes mellitus, or hyperthyroidism) may cause the litter box to become soiled more quickly than expected. The increased soil and odor may cause cats to find a bathroom more to their liking.

• Many cats that do not mark their territory with urine, even if exposed to intruding cats, may begin to do so if a condition like hyperthyroidism develops.

• Cats with painful arthritis may have difficulty gaining access to a litter box, especially if negotiating stairs is required. Even climbing into the box may be painful for such cats; urinating or defecating in an inappropriate location is the natural result.

• Older cats may be more sensitive to changes in the household since their ability to adapt to unfamiliar situations diminishes with age.

The take-home message? Never assume that changes you see in your older cat are simply due to old age, and therefore untreatable. Any alteration in your cat's behavior or physical condition should alert you to contact your veterinarian.